Lands on Schedule C, line 9 — Car and truck expenses, with Part IV
If you are reimbursed for mileage by an employer, this article is not for you. This is for people deducting their own business driving.
Plenty of guides tell you what to put in a mileage log. Far fewer tell you what makes one fail — and a log usually fails for reasons that have nothing to do with how many trips are in it.
The short answer
| The log fails because | Not because |
|---|---|
| It was written months later | entries are missing |
| Nothing ties an entry to a date | the total is too high |
| No entry says why you drove | you used an app instead of paper |
| It claims 100% business use of a shared car | you rounded once |
The sentence that governs all of it, from Publication 463:
"A timely kept record has more value than a statement prepared later when there is generally a lack of accurate recall."
Not "is required". Has more value. A reconstruction is not void — it is weaker, and it gets weaker the further it is from the driving.
The permission nobody quotes
The same passage contains something most guides skip, and it is the useful half:
"You should record the elements of an expense or of a business use at or near the time of the expense or use... You don't need to write down the elements of every expense on the day of the expense. If you maintain a log on a weekly basis that accounts for use during the week, the log is considered a timely kept record."
So the standard is not daily discipline. Weekly is explicitly enough.
That matters, because "log every trip the moment it ends" is the advice that makes people give up in February. A weekly review of the week's driving meets the standard the publication actually sets.
Four ways a log stops being worth anything
1. It was built from memory in April
The most common failure and the hardest to repair. Once you are reconstructing, you are relying on exactly what the publication says is absent — accurate recall — and you are doing it for a year you can no longer verify.
2. Nothing carries a date
This is newly expensive. 2026 has two business standard mileage rates: 72.5 cents per mile from January 1 through June 30, and 76 cents from July 1 through December 31.
A log that records 14,000 business miles with no dates cannot be priced. Not "is harder to price" — cannot, because the correct figure depends on which side of July 1 each trip fell.
A total is not a record. A dated list is.
3. No entry says why you drove
Publication 463 wants the record supported by evidence for each element of the expense, and business purpose is one of them.
"Business" is not a purpose. "Client meeting — Oak Street" is. This is the field an app cannot fill for you: it knows where you went and how far, and has no idea whether it was a delivery or your sister's house.
Write the purpose while you still remember it. That is most of what "timely" is protecting.
4. It claims the whole car
If a vehicle is also used personally — and for most independent workers it is — only the business portion is deductible. A log showing 100% business use of the only car in a one-car household is the single hardest claim to support, and it invites scrutiny of everything around it.
Recording personal trips, or at least marking them, costs nothing and makes the business figure credible rather than assumed.
What an entry actually contains
Five things, per trip:
| Element | Example |
|---|---|
| Date | 14 March |
| From | Home office |
| To | Oak Street project site |
| Business purpose | Client walkthrough, phase two |
| Business miles | 23 |
Publication 463 says to keep this in "an account book, diary, log, statement of expense, trip sheets, or similar record", supported by documentary evidence. A spreadsheet is a log. A notebook in the glovebox is a log. The format was never the point.
And one decision that closes a door
If you claim section 179, the special depreciation allowance, or MACRS depreciation on a vehicle, Publication 463 rules out the standard mileage rate for that vehicle. Not for that year — for that vehicle.
Which means the deduction method is decided the first time you write off the car, often before anyone has thought about mileage at all. Worth knowing before it is decided for you.
The routine
- One capture method. App, spreadsheet, notebook — pick one and stop comparing.
- Add the business purpose the same day, even if you add nothing else. It is the field that decays fastest.
- Fifteen minutes weekly, which is the standard the publication sets.
- Keep the date on every entry, because in 2026 the date is what prices the mile.
- Mark personal trips rather than omitting them.
- Keep parking and tolls separately — they are not inside the standard rate.
A log works because of the routine. Nothing about the logo on the app changes that.
Track it now. Thank yourself in April.
Common questions
Do I have to write down every trip the day it happens?
Can I reconstruct my mileage at the end of the year?
Is my app's trip history enough on its own?
Why does the date matter so much in 2026?
What actually belongs in an entry?
My car is also the family car. Does that disqualify the deduction?
Can I use the standard mileage rate on a vehicle I depreciated?
This article is for educational purposes only and does not constitute tax, legal, or financial advice. Consult a qualified tax professional about your situation.